Nylon can be dyed with acid or cationic dyes to give colored yarns which may be used in fabrics or carpets. Recently, yarn producers have begun incorporating colored pigments into nylon yarns to improve their resistance to degrading and fading in ultraviolet light, to give improved resistance to chemicals and noxious fumes and to give permanent coloration which is not removed by washing. While some pigments can be mixed easily into the nylon without adversely affecting the filament spinning operation, most pigments--and particularly organics--cause some difficulties while being mixed into the nylon or in subsequent melt-spinning and drawing operations. In general, organic pigments cross-link nylon, change its viscosity, form spherulites which weaken the fibers, and require increased draw tension resulting in increased filament breaks.
European Patent Publication No. 0373655 ("Anton et al"), published Jun. 20, 1990, and incorporated herein by reference, discloses processes for making stain-resistant, pigment-colored fibers with acceptable levels of spinning performance. Those processes involve forming a random nylon copolymer made with up to 4.0 weight percent of a cationic dye additive such as 5-sulfoisophthalic acid or its salts, adding up to 4.5 weight percent of a pigment concentrate to the copolymer, and melt-spinning the pigment/polymer blend. Certain pigments, however, remain very difficult to spin even using the copolymers disclosed therein.
Ways of reducing the impact of such pigments on nylon spinning and drawing performance would permit the use of a wider selection of colored pigments, both organic and inorganic, would enable fiber products to offer a complete range of styling colors without encountering serious product deficiencies or operating difficulties with any of them, and would allow for the production of high tenacity pigmented nylon fibers.